1. Field of the Invention
This invention relates to a flywheel device for a prime mover, such as a flywheel having a torsional vibration damper for use with a vehicle driving system, which is capable of transmitting torque from the prime mover while reducing variation in the torque and damping torsional vibration.
2. Description of the Prior Art
Conventionally, a flywheel device of the above-mentioned kind has been proposed e.g. by Japanese Utility Model Registration Publication (Kokoku) No. 5712273. This flywheel device is comprised of a flywheel body and a torsional vibration damper (hereinafter referred to as xe2x80x9cthe torsional damperxe2x80x9d) which are assembled into a unit. The flywheel device is arranged between the engine and the clutch. The flywheel body includes a disc-shaped base portion, and a protrusion which protrudes toward the clutch from an outer peripheral end of the base portion. The base portion has an engine crankshaft mounted in a central portion thereof, and a bearing fitted in a central portion of a clutch-side end thereof, for rotatably supporting an input shaft of the clutch.
The torsional damper is comprised of a hub splined to the input shaft of the clutch, two plates integrally fixed to each other in a state holding a flange portion extending radially outward from the hub, coil springs received between the two plates for damping torsional vibration, and grease. Further, one of the plates has a radial outer end rigidly fixed to the protrusion of the flywheel body by a plurality of bolts. The construction described above causes torque from the engine to be transmitted to the input shaft of the clutch via the flywheel body and the torsional damper. In the transmission process, the flywheel body reduces variation in the torque, and the torsional damper damps torsional vibration.
According to the above conventional flywheel device, since the bearing is fitted in the flywheel body, the central portion of the flywheel body is required to be thick enough to receive the bearing therein, and further, since one of the plates of the torsional damper is fixed to the protrusion protruding toward the clutch, the axial size of the whole flywheel device is inevitably increased.
It is an object of the invention to provide a flywheel device for a prime mover, which can be made compact in the axial size thereof and have an effectively increased inertial mass.
To attain the above object, the present invention provides a flywheel device for a prime mover, which is arranged between an output shaft and a driven shaft of the prime mover,
the flywheel device comprising:
a plate having a fitting portion in a radially outer portion thereof and mounted to the output shaft in a manner concentric therewith; and
an inertial mass member having an annular shape, the inertial mass member having a fitting portion which is fitted to the fitting portion of the plate, whereby the inertial mass member is concentrically attached to the plate, for transmitting torque from the prime mover to the driven shaft while reducing variation in the torque.
According to this flywheel device, the inertial mass member transmits torque from the prime mover to the driven shaft while reducing variation in the torque. Further, the plate is mounted to the output shaft in a manner concentric therewith, and the inertial mass member has an annular shape and is concentrically attached to the plate via the fitting portion thereof which is fitted to the fitting portion in the radially outer portion of the plate. The inertial mass member is thus centered with respect to the output shaft simply by fitting the fitting portion of the inertial mass member and the fitting portion of the plate to each other. This makes it possible to center the inertial mass member with ease and accuracy when the flywheel device is attached to the output shaft. Further, since the inertial mass member annular in shape is attached to the radially outer portion of the plate, it is possible to effectively increase the inertial mass of the flywheel device and at the same time make the whole device compact in axial size. This makes it possible to attain reduction of the total weight of the inertial mass member and the plate and securing of the inertial mass and the moment of inertia, in a properly balanced manner. Further, since a member corresponding to the conventional flywheel body is formed by assembling the two components of the inertial mass member and the plate, it is possible to increase the freedom of arrangement thereof in comparison with the conventional flywheel body.
Preferably, the flywheel device further comprises a linkage connecting between a portion of the inertial mass member radially inward of the fitting portion thereof and the driven shaft, and a damping mechanism arranged in the linkage, for transmitting the torque from the prime mover to the driven shaft while damping torsional vibration thereof.
According to this preferred embodiment, the torque from the prime mover is transmitted to the driven shaft via the plate, the inertial mass member, the linkage, and the damping mechanism while the damping mechanism damping torsional vibration. Further, the damping mechanism is arranged in the linkage which is connected to the portion of the inertial mass member radially inward of the fitting portion. Therefore, the fitting portion of the inertial mass member and the damping mechanism are prevented from being axially arranged side by side, thereby making it possible to make the whole device more compact in axial size. Furthermore, the fitting portion of the inertial mass member is arranged at a location outward of the linkage and the damping mechanism, so that the fitting portion can be formed in a simplified manner without being adversely affected by the constructions and shapes of the linkage and the damping mechanism or being obstructed by them.
Preferably, the damping mechanism comprises at least one coil spring, and the linkage includes a pair of spring holder plates for holding the at least one coil spring in a spring chamber formed therebetween.
According to this preferred embodiment, it is possible to damp the torsional vibration occurring when torque from the prime mover is transmitted to the driven shaft, by using the at least one coil spring which is a relatively simple and easily available component. Further, the same effects as described above can be obtained by the relatively simple construction that the at least one coil spring is accommodated in the spring chamber formed between the pair of spring holder plates.
More preferably, the damping mechanism further comprises a pair of friction discs each having a predetermined coefficient of kinetic friction, grease contained in the spring chamber and having a predetermined coefficient of viscosity, the at least one coil spring having a predetermined spring modulus, and the predetermined coefficient of kinetic friction of each friction disc, the coefficient of viscosity of the grease, and the spring modulus of each coil spring are selected such that a rotational vibration system including the primer mover and the driven shaft has a resonance frequency which is outside a range of values thereof corresponding to a predetermined rotational speed region of the prime mover.
Further preferably, the at least one coil spring comprises at least two kinds of coil springs arranged such that the at least two kinds of coil springs start to be compressed at respective relative rotational angles of the output shaft to the driven shaft.
Further preferably, the grease fills part of a volume of the spring chamber.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.